'Using current technology to look for early signs of a virus or a disease can be like finding the proverbial needle in a haystack,' said Professor Stevens. 'Our new detection system, is highly innovative; it is not only an affordable methodology that will greatly improve the standard of living of patients with HIV infection in low income countries, but as it is also more sensitive than any existing conventional test, it will also enable the ultrasensitive detection of disease biomarkers, i.e. biological indicators of disease, with the naked eye.'

Commenting on the groundbreaking result, Dr de la Rica said: 'We have abandoned principles within the existing methodological framework to propose a radically new line of investigation. The test will allow us to detect HIV infection in patients that were previously undetectable, and costs will be significantly cheaper.'

The researchers believe the novel test could prove beneficial for laboratories that do not have many resources. They said numerical analysis would not have to be performed to count the number of viruses per collected blood sample to determine an HIV case. A change in the colour of the analysed samples would be enough to confirm or discard infections, according to them.

Commercialisation of the test is possible if more research is conducted. But the researchers said they are hopeful that their research can be translated to the clinical setting and point-of-care use.

Lowering the limit of detection is key to the design of sensors needed for food safety regulations environmental policies and the diagnosis of severe diseases. However, because conventional transducers generate a signal that is directly proportional to the concentration of the target molecule, ultralow concentrations of the molecule result in variations in the physical properties of the sensor that are tiny, and therefore difficult to detect with confidence. Here we present a signal-generation mechanism that redefines the limit of detection of nanoparticle sensors by inducing a signal that is larger when the target molecule is less concentrated. The key step to achieve this inverse sensitivity is to use an enzyme that controls the rate of nucleation of silver nanocrystals on plasmonic transducers. We demonstrate the outstanding sensitivity and robustness of this approach by detecting the cancer biomarker prostate-specific antigen down to 10^−18 g ml−1 (4 × 10^−20 M) in whole serum.